import matplotlib.pyplot as plt

frequencies = [3, 7, 25]
amplitudes = [20, 10, 2]

# create frequency domain graph
plt.figure(figsize=(8, 4))
for f, a in zip(frequencies, amplitudes):
    plt.plot([f, f], [0, a], 'b-', linewidth=2)  
plt.scatter(frequencies, amplitudes, color='blue')  
plt.title('Frequency Domain Representation')
plt.xlabel('Frequency (Hz)')
plt.ylabel('Amplitude (V)')
plt.grid(True, linestyle='--', alpha=0.6)
plt.xticks(frequencies)
plt.ylim(0, 21)
plt.xlim(0, 30)

plt.show()